1. Field of the invention
The present invention relates to a welding power control device and a method for a consumable-electrode type pulse arc welding used for welding with an automatically supplied consumable electrode using a shield gas of which the major component is carbon dioxide, and relates specifically to such method and apparatus whereby the spatter that occurs during welding is greatly reduced to stabilize welding results and to obtain a good welded surface.
2. Description of the prior art
Heretofore, for the consumable electrode-type pulsed arc welding method, a shield gas of an inert gas was employed, e.g., having argon gas as its main component. In this method, a peak current larger than a value of the critical current (above which spray transfer is possible) and a base current lower than the critical current (for maintaining an arc) are alternately supplied at a frequency corresponding to a consumable electrode (hereinafter, referred to as "wire") feeding speed. Thereby, spray transfer can be performed with a lower average current than the DC welding method, and the droplet transfer is performed during the period of base current such that a least arc force acts on the droplet. Consequently, spatter is significantly reduced.
However, the above-mentioned pulsed arc welding method is restricted in the choice of shielding gas composition, because the spatter reducing effect becomes weaker when the content ratio of carbon dioxide in a shielding gas exceeds 30%. Therefore, a large amount of argon gas is consumed. Accordingly, the cost of the shielding gas has been a main cause of the high running cost of the pulsed arc welding method.
While consumable electrode-type pulse arc welding methods and corresponding apparatuses (hereinafter referred to as "consumable electrode-welder) are essential processing tools for modern manufacturing industries, consumable-electrode welders that produce less spatter and provide stable operation are in demand.
Conventional consumable electrode-type pulsed arc welding apparatuses (welders) that use a shield gas of which the major component is carbon dioxide are typically controlled by a welding power (output) control method such as that described in Japanese Laid-Open (Examined) Patent Publication No. H2-31630. Specifically, in this document, an arc is generated by supplying the peak current and the base current alternately, letting a droplet detach by a pinch force at the initial stage of the peak current duration, and subsequently forming molten metal by melting the tip part of the wire (electrode). The formed molten metal then; detaches during the next peak current duration.
However, in the power control scheme in this consumable electrode-type pulsed arc welder, there is a danger of detached droplets becoming spatter, because the droplet detached during the peak current duration is subject to a strong arc force from to the peak current.